Effects Of Plasma Spraying Technology Parameter On Microstructure And Bonding Strength Of ZrB₂-SiC-ZrC Coating

ZrB₂-SiC-ZrC composite was widely used in aerospace,military and other fields for its excellent oxidation resistance and ablation resistance.In order to improve the oxidation resistance and ablation resistance of ZrC composite ceramics in ultra high temperature environment,using Zr,B4 C and Si powders as raw materials prepared ZrB₂-20vol%SiC-6.015vol%ZrC composite coatings on ZrC composite ceramics surface by plasma spraying?PS?technology.Researched the effect of different spraying technology parameters on the phase,microstructure and properties of the coating and find the best spraying technology parameters to obtain the high quality composite coatings.The ZrB₂/20vol%SiC/6.015vol%ZrC spraying composite powders was prepared by vacuum hot press sintering method,which contained a small amount of ZrO₂ and SiO₂ in addition to ZrB₂,SiC and ZrC.In the sintering process,at first,Zr with B4 C reacted to form ZrB₂ and free C atoms;then Zr with free C atoms reacted to form ZrC;Finally,Si with residual B4 C and generate parts of the ZrC reacted to form ZrB₂ and SiC,until the raw materials were exhausted.After crushing and vibratings creening of the sintering samples to select the particle size of 50 ?m¹20 ?m particles as the spraying powders.When it is changing of the spraying current,spraying distance and send powder gas flow rate,the phase composition of the composite coating will not change.The phase composition of the composite coatings which is highly consistent with the phase composition of sintering samples,only a small increase of oxides?ZrO₂,SiO₂?.The surface,cross section and fracture surface of the coatings were analyzed by SEM.The results showed that increasing the spraying current,spraying particles melt more fully,the surface of the coating moresmooth,the relative density of the coating was improved obviously in the proper range;the spraying distance which has also an impact on the quality of the coating,the spraying distance is too small,the melting degree of sprayed particles was decreased,the connected between particles loose,and the porosity was increased;the spraying distance is too large,the probability increases of the gas was involved into melt droplet,the porosity was increased.Too large or too small send powder gas flow rate could also reduce the melting degree of spraying particles,resulting in the thickness of coating was uneven and the relative density of coating was decreased.The bonding strength of the composite coatings were tested by the method of coating adhesion dual stretching.The results showed that the bonding strength of the composite coating increases with the increase of spraying current,and decreases with the increase of the spraying distance,and increases with the increase of send powder gas flow rate within a certain range.In the scope of the study,the best spraying technology parameters are spraying current 600 A,spraying distance 80 mm,send powder gas flow rate 2.5 L/min.